private Task <bool> WaitToReadAsync(CancellationToken cancellationToken = default(CancellationToken))
{
// If there are any items, readers can try to get them.
if (!_items.IsEmpty)
{
return(ChannelUtilities.TrueTask);
}
lock (SyncObj)
{
AssertInvariants();
// Try again to read now that we're synchronized with writers.
if (!_items.IsEmpty)
{
return(ChannelUtilities.TrueTask);
}
// There are no items, so if we're done writing, there's never going to be data available.
if (_doneWriting != null)
{
return(_doneWriting != ChannelUtilities.DoneWritingSentinel ?
Task.FromException <bool>(_doneWriting) :
ChannelUtilities.FalseTask);
}
// Queue the waiter
return(ChannelUtilities.GetOrCreateWaiter(ref _waitingReaders, _runContinuationsAsynchronously, cancellationToken));
}
}
private ValueAwaiter <T> GetAwaiterCore()
{
lock (SyncObj)
{
// Now that we hold the lock, try reading again.
T item;
if (TryRead(out item))
{
return(new ValueAwaiter <T>(item));
}
// If no more items will be written, fail the read.
if (_doneWriting != null)
{
return(new ValueAwaiter <T>(ChannelUtilities.GetInvalidCompletionValueTask <T>(_doneWriting)));
}
Debug.Assert(_blockedReader == null || ((_blockedReader as ReaderInteractor <T>)?.Task.IsCanceled ?? false),
"Incorrect usage; multiple outstanding reads were issued against this single-consumer channel");
// Store the reader to be completed by a writer.
_blockedReader = _awaiter ?? (_awaiter = new AutoResetAwaiter <T>(_runContinuationsAsynchronously));
return(new ValueAwaiter <T>(_awaiter));
}
}
private ValueTask <T> ReadAsync(CancellationToken cancellationToken = default(CancellationToken))
{
// Fast-path cancellation check
if (cancellationToken.IsCancellationRequested)
{
return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken)));
}
lock (SyncObj)
{
AssertInvariants();
// If there are any items, hand one back.
if (!_items.IsEmpty)
{
return(new ValueTask <T>(DequeueItemAndPostProcess()));
}
// There weren't any items. If we're done writing so that there
// will never be more items, fail.
if (_doneWriting != null)
{
return(ChannelUtilities.GetErrorValueTask <T>(_doneWriting));
}
// Otherwise, queue the reader.
var reader = ReaderInteractor <T> .Create(_runContinuationsAsynchronously, cancellationToken);
_blockedReaders.EnqueueTail(reader);
return(new ValueTask <T>(reader.Task));
}
}
private Task <bool> WaitToReadAsync(CancellationToken cancellationToken = default(CancellationToken))
{
if (cancellationToken.IsCancellationRequested)
{
return(Task.FromCanceled <bool>(cancellationToken));
}
lock (SyncObj)
{
AssertInvariants();
// If there are any items available, a read is possible.
if (!_items.IsEmpty)
{
return(ChannelUtilities.TrueTask);
}
// There were no items available, so if we're done writing, a read will never be possible.
if (_doneWriting != null)
{
return(ChannelUtilities.FalseTask);
}
// There were no items available, but there could be in the future, so ensure
// there's a blocked reader task and return it.
return(ChannelUtilities.GetOrCreateWaiter(ref _waitingReaders, _runContinuationsAsynchronously, cancellationToken));
}
}
private ValueTask <T> ReadAsyncCore(CancellationToken cancellationToken)
{
if (cancellationToken.IsCancellationRequested)
{
return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken)));
}
lock (SyncObj)
{
AssertInvariants();
// If we're already completed, nothing to read.
if (_completion.Task.IsCompleted)
{
return(new ValueTask <T>(
_completion.Task.IsCanceled ? Task.FromCanceled <T>(new CancellationToken(true)) :
Task.FromException <T>(
_completion.Task.IsFaulted ?
ChannelUtilities.CreateInvalidCompletionException(_completion.Task.Exception.InnerException) :
ChannelUtilities.CreateInvalidCompletionException())));
}
// If there are any blocked writers, find one to pair up with
// and get its data. Writers that got canceled will remain in the queue,
// so we need to loop to skip past them.
while (!_blockedWriters.IsEmpty)
{
WriterInteractor <T> w = _blockedWriters.DequeueHead();
if (w.Success(default))
private Task <bool> WaitToWriteAsync(CancellationToken cancellationToken = default(CancellationToken))
{
if (cancellationToken.IsCancellationRequested)
{
return(Task.FromCanceled <bool>(cancellationToken));
}
lock (SyncObj)
{
AssertInvariants();
// If we're done writing, no writes will ever succeed.
if (_doneWriting != null)
{
return(ChannelUtilities.FalseTask);
}
// If there's space to write, a write is possible.
// And if the mode involves dropping, we can always write, as even if it's
// full we'll just drop an element to make room.
if (_items.Count < _bufferedCapacity || _mode != BoundedChannelFullMode.Wait)
{
return(ChannelUtilities.TrueTask);
}
// We're still allowed to write, but there's no space, so ensure a waiter is queued and return it.
return(ChannelUtilities.GetOrCreateWaiter(ref _waitingWriters, true, cancellationToken));
}
}
/// <summary>Dequeues an item, and then fixes up our state around writers and completion.</summary>
/// <returns>The dequeued item.</returns>
private T DequeueItemAndPostProcess()
{
Debug.Assert(Monitor.IsEntered(SyncObj));
// Dequeue an item.
T item = _items.DequeueHead();
// If we're now empty and we're done writing, complete the channel.
if (_doneWriting != null && _items.IsEmpty)
{
ChannelUtilities.Complete(_completion, _doneWriting);
}
// If there are any writers blocked, there's now room for at least one
// to be promoted to have its item moved into the items queue. We need
// to loop while trying to complete the writer in order to find one that
// hasn't yet been canceled (canceled writers transition to canceled but
// remain in the physical queue).
while (!_blockedWriters.IsEmpty)
{
WriterInteractor <T> w = _blockedWriters.DequeueHead();
if (w.Success(default(VoidResult)))
{
_items.EnqueueTail(w.Item);
return(item);
}
}
// There was no blocked writer, so see if there's a WaitToWriteAsync
// we should wake up.
ChannelUtilities.WakeUpWaiters(ref _waitingWriters, result: true);
// Return the item
return(item);
}
private ValueTask <T> ReadAsyncCore(CancellationToken cancellationToken)
{
if (cancellationToken.IsCancellationRequested)
{
return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken)));
}
lock (SyncObj)
{
// Now that we hold the lock, try reading again.
T item;
if (TryRead(out item))
{
return(new ValueTask <T>(item));
}
// If no more items will be written, fail the read.
if (_doneWriting != null)
{
return(ChannelUtilities.GetInvalidCompletionValueTask <T>(_doneWriting));
}
Debug.Assert(_blockedReader == null || ((_blockedReader as ReaderInteractor <T>)?.Task.IsCanceled ?? false),
"Incorrect usage; multiple outstanding reads were issued against this single-consumer channel");
// Store the reader to be completed by a writer.
ReaderInteractor <T> reader = ReaderInteractor <T> .Create(_runContinuationsAsynchronously, cancellationToken);
_blockedReader = reader;
return(new ValueTask <T>(reader.Task));
}
}
/// <summary>Mark the channel as being complete, meaning no more items will be written to it.</summary>
/// <param name="error">Optional Exception indicating a failure that's causing the channel to complete.</param>
/// <exception cref="InvalidOperationException">The channel has already been marked as complete.</exception>
public void Complete(Exception error = null)
{
if (!TryComplete(error))
{
throw ChannelUtilities.CreateInvalidCompletionException();
}
}
private Task WriteAsync(T item, CancellationToken cancellationToken = default)
{
// Writing always succeeds (unless we've already completed writing or cancellation has been requested),
// so just TryWrite and return a completed task.
return
(cancellationToken.IsCancellationRequested ? Task.FromCanceled(cancellationToken) :
TryWrite(item) ? Task.CompletedTask :
Task.FromException(ChannelUtilities.CreateInvalidCompletionException(_doneWriting)));
}
private bool TryRead(out T item)
{
if (_items.TryDequeue(out item))
{
if (_doneWriting != null && _items.IsEmpty)
{
ChannelUtilities.Complete(_completion, _doneWriting);
}
return(true);
}
return(false);
}
private bool TryRead(out T item)
{
// Dequeue an item if we can
if (_items.TryDequeue(out item))
{
if (_doneWriting != null && _items.IsEmpty)
{
// If we've now emptied the items queue and we're not getting any more, complete.
ChannelUtilities.Complete(_completion, _doneWriting);
}
return(true);
}
item = default(T);
return(false);
}
private ValueTask <T> ReadAsyncCore(CancellationToken cancellationToken)
{
if (cancellationToken.IsCancellationRequested)
{
return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken)));
}
lock (SyncObj)
{
AssertInvariants();
// If we're already completed, nothing to read.
if (_completion.Task.IsCompleted)
{
return(new ValueTask <T>(
_completion.Task.IsCanceled ? Task.FromCanceled <T>(new CancellationToken(true)) :
Task.FromException <T>(
_completion.Task.IsFaulted ?
ChannelUtilities.CreateInvalidCompletionException(_completion.Task.Exception.InnerException) :
ChannelUtilities.CreateInvalidCompletionException())));
}
// If there are any blocked writers, find one to pair up with
// and get its data. Writers that got canceled will remain in the queue,
// so we need to loop to skip past them.
while (!_blockedWriters.IsEmpty)
{
WriterInteractor <T> w = _blockedWriters.DequeueHead();
if (w.Success(default(VoidResult)))
{
return(new ValueTask <T>(w.Item));
}
}
// No writer found to pair with. Queue the reader.
var r = ReaderInteractor <T> .Create(true, cancellationToken);
_blockedReaders.EnqueueTail(r);
// And let any waiting writers know it's their lucky day.
ChannelUtilities.WakeUpWaiters(ref _waitingWriters, result: true);
return(new ValueTask <T>(r.Task));
}
}
private Task WriteAsync(T item, CancellationToken cancellationToken = default(CancellationToken))
{
if (cancellationToken.IsCancellationRequested)
{
return(Task.FromCanceled(cancellationToken));
}
lock (SyncObj)
{
// Fail if we've already completed
if (_completion.Task.IsCompleted)
{
return
(_completion.Task.IsCanceled ? Task.FromCanceled <T>(new CancellationToken(true)) :
Task.FromException <T>(
_completion.Task.IsFaulted ?
ChannelUtilities.CreateInvalidCompletionException(_completion.Task.Exception.InnerException) :
ChannelUtilities.CreateInvalidCompletionException()));
}
// Try to find a reader to pair with. Canceled readers remain in the queue,
// so we need to loop until we find one.
while (!_blockedReaders.IsEmpty)
{
ReaderInteractor <T> r = _blockedReaders.DequeueHead();
if (r.Success(item))
{
return(Task.CompletedTask);
}
}
// No reader was available. Queue the writer.
var w = WriterInteractor <T> .Create(true, cancellationToken, item);
_blockedWriters.EnqueueTail(w);
// And let any waiting readers know it's their lucky day.
ChannelUtilities.WakeUpWaiters(ref _waitingReaders, result: true);
return(w.Task);
}
}
private bool TryComplete(Exception error = null)
{
bool completeTask;
lock (SyncObj)
{
AssertInvariants();
// If we've already marked the channel as completed, bail.
if (_doneWriting != null)
{
return(false);
}
// Mark that we're done writing.
_doneWriting = error ?? ChannelUtilities.DoneWritingSentinel;
completeTask = _items.IsEmpty;
}
// If there are no items in the queue, complete the channel's task,
// as no more data can possibly arrive at this point. We do this outside
// of the lock in case we'll be running synchronous completions, and we
// do it before completing blocked/waiting readers, so that when they
// wake up they'll see the task as being completed.
if (completeTask)
{
ChannelUtilities.Complete(_completion, error);
}
// At this point, _blockedReaders/Writers and _waitingReaders/Writers will not be mutated:
// they're only mutated by readers/writers while holding the lock, and only if _doneWriting is null.
// We also know that only one thread (this one) will ever get here, as only that thread
// will be the one to transition from _doneWriting false to true. As such, we can
// freely manipulate _blockedReaders and _waitingReaders without any concurrency concerns.
ChannelUtilities.FailInteractors <ReaderInteractor <T>, T>(_blockedReaders, error);
ChannelUtilities.FailInteractors <WriterInteractor <T>, VoidResult>(_blockedWriters, error);
ChannelUtilities.WakeUpWaiters(ref _waitingReaders, result: false);
ChannelUtilities.WakeUpWaiters(ref _waitingWriters, result: false);
// Successfully transitioned to completed.
return(true);
}
private Task <bool> WaitToWriteAsync(CancellationToken cancellationToken = default(CancellationToken))
{
lock (SyncObj)
{
// If we're done writing, fail.
if (_completion.Task.IsCompleted)
{
return(ChannelUtilities.FalseTask);
}
// If there's a blocked reader, we can write
if (!_blockedReaders.IsEmpty)
{
return(ChannelUtilities.TrueTask);
}
// Otherwise, queue the writer
return(ChannelUtilities.GetOrCreateWaiter(ref _waitingWriters, true, cancellationToken));
}
}
/// <summary>Dequeues an item, and then fixes up our state around writers and completion.</summary>
/// <returns>The dequeued item.</returns>
private T DequeueItemAndPostProcess()
{
Debug.Assert(Monitor.IsEntered(SyncObj));
// Dequeue an item.
T item = _items.DequeueHead();
// If we're now empty and we're done writing, complete the channel.
if (_doneWriting != null && _items.IsEmpty)
{
ChannelUtilities.Complete(_completion, _doneWriting);
}
// If there are any writers blocked, there's now room for at least one
// to be promoted to have its item moved into the items queue. We need
// to loop while trying to complete the writer in order to find one that
// hasn't yet been canceled (canceled writers transition to canceled but
// remain in the physical queue).
while (!_blockedWriters.IsEmpty)
{
WriterInteractor <T> w = _blockedWriters.DequeueHead();
if (w.Success(default))
private Task <bool> WaitToReadAsync(CancellationToken cancellationToken = default(CancellationToken))
{
lock (SyncObj)
{
// If we're done writing, fail.
if (_completion.Task.IsCompleted)
{
return(_completion.Task.IsFaulted ?
Task.FromException <bool>(_completion.Task.Exception.InnerException) :
ChannelUtilities.FalseTask);
}
// If there's a blocked writer, we can read.
if (!_blockedWriters.IsEmpty)
{
return(ChannelUtilities.TrueTask);
}
// Otherwise, queue the waiter.
return(ChannelUtilities.GetOrCreateWaiter(ref _waitingReaders, true, cancellationToken));
}
}
private ValueTask <T> ReadAsyncCore(CancellationToken cancellationToken)
{
if (cancellationToken.IsCancellationRequested)
{
return(new ValueTask <T>(Task.FromCanceled <T>(cancellationToken)));
}
lock (SyncObj)
{
AssertInvariants();
// If there are any items, return one.
T item;
if (_items.TryDequeue(out item))
{
// Dequeue an item
if (_doneWriting != null && _items.IsEmpty)
{
// If we've now emptied the items queue and we're not getting any more, complete.
ChannelUtilities.Complete(_completion, _doneWriting);
}
return(new ValueTask <T>(item));
}
// There are no items, so if we're done writing, fail.
if (_doneWriting != null)
{
return(ChannelUtilities.GetInvalidCompletionValueTask <T>(_doneWriting));
}
// Otherwise, queue the reader.
ReaderInteractor <T> reader = ReaderInteractor <T> .Create(_runContinuationsAsynchronously, cancellationToken);
_blockedReaders.EnqueueTail(reader);
return(new ValueTask <T>(reader.Task));
}
}
private bool TryComplete(Exception error = null)
{
lock (SyncObj)
{
AssertInvariants();
// Mark the channel as being done. Since there's no buffered data, we can complete immediately.
if (_completion.Task.IsCompleted)
{
return(false);
}
ChannelUtilities.Complete(_completion, error);
// Fail any blocked readers/writers, as there will be no writers/readers to pair them with.
ChannelUtilities.FailInteractors <ReaderInteractor <T>, T>(_blockedReaders, ChannelUtilities.CreateInvalidCompletionException(error));
ChannelUtilities.FailInteractors <WriterInteractor <T>, VoidResult>(_blockedWriters, ChannelUtilities.CreateInvalidCompletionException(error));
// Let any waiting readers and writers know there won't be any more data
ChannelUtilities.WakeUpWaiters(ref _waitingReaders, result: false, error: error);
ChannelUtilities.WakeUpWaiters(ref _waitingWriters, result: false, error: error);
}
return(true);
}
private Task WriteAsync(T item, CancellationToken cancellationToken = default(CancellationToken))
{
if (cancellationToken.IsCancellationRequested)
{
return(Task.FromCanceled(cancellationToken));
}
ReaderInteractor <T> blockedReader = null;
ReaderInteractor <bool> waitingReaders = null;
lock (SyncObj)
{
AssertInvariants();
// If we're done writing, trying to write is an error.
if (_doneWriting != null)
{
return(Task.FromException(ChannelUtilities.CreateInvalidCompletionException()));
}
// Get the number of items in the channel currently.
int count = _items.Count;
if (count == 0)
{
// There are no items in the channel, which means we may have blocked/waiting readers.
// If there are any blocked readers, find one that's not canceled
// and store it to complete outside of the lock, in case it has
// continuations that'll run synchronously
while (!_blockedReaders.IsEmpty)
{
ReaderInteractor <T> r = _blockedReaders.DequeueHead();
r.UnregisterCancellation(); // ensure that once we grab it, we own its completion
if (!r.Task.IsCompleted)
{
blockedReader = r;
break;
}
}
if (blockedReader == null)
{
// If there wasn't a blocked reader, then store the item. If no one's waiting
// to be notified about a 0-to-1 transition, we're done.
_items.EnqueueTail(item);
waitingReaders = _waitingReaders;
if (waitingReaders == null)
{
return(ChannelUtilities.TrueTask);
}
_waitingReaders = null;
}
}
else if (count < _bufferedCapacity)
{
// There's room in the channel. Since we're not transitioning from 0-to-1 and
// since there's room, we can simply store the item and exit without having to
// worry about blocked/waiting readers.
_items.EnqueueTail(item);
return(ChannelUtilities.TrueTask);
}
else if (_mode == BoundedChannelFullMode.Wait)
{
// The channel is full and we're in a wait mode.
// Queue the writer.
var writer = WriterInteractor <T> .Create(true, cancellationToken, item);
_blockedWriters.EnqueueTail(writer);
return(writer.Task);
}
else
{
// The channel is full, and we're in a dropping mode.
// Drop either the oldest or the newest and write the new item.
T droppedItem = _mode == BoundedChannelFullMode.DropNewest ?
_items.DequeueTail() :
_items.DequeueHead();
_items.EnqueueTail(item);
return(ChannelUtilities.TrueTask);
}
}
// We either wrote the item already, or we're transfering it to the blocked reader we grabbed.
if (blockedReader != null)
{
// Transfer the written item to the blocked reader.
bool success = blockedReader.Success(item);
Debug.Assert(success, "We should always be able to complete the reader.");
}
else
{
// We stored an item bringing the count up from 0 to 1. Alert
// any waiting readers that there may be something for them to consume.
// Since we're no longer holding the lock, it's possible we'll end up
// waking readers that have since come in.
waitingReaders.Success(item: true);
}
return(ChannelUtilities.TrueTask);
}
private bool TryComplete(Exception error = null)
{
object blockedReader = null;
ReaderInteractor <bool> waitingReader = null;
bool completeTask = false;
lock (SyncObj)
{
// If we're already marked as complete, there's nothing more to do.
if (_doneWriting != null)
{
return(false);
}
// Mark as complete for writing.
_doneWriting = error ?? ChannelUtilities.DoneWritingSentinel;
// If we have no more items remaining, then the channel needs to be marked as completed
// and readers need to be informed they'll never get another item. All of that needs
// to happen outside of the lock to avoid invoking continuations under the lock.
if (_items.IsEmpty)
{
completeTask = true;
if (_blockedReader != null)
{
blockedReader = _blockedReader;
_blockedReader = null;
}
if (_waitingReader != null)
{
waitingReader = _waitingReader;
_waitingReader = null;
}
}
}
// Complete the channel task if necessary
if (completeTask)
{
ChannelUtilities.Complete(_completion, error);
}
Debug.Assert(blockedReader == null || waitingReader == null, "There should only ever be at most one reader.");
// Complete a blocked reader if necessary
if (blockedReader != null)
{
error = ChannelUtilities.CreateInvalidCompletionException(error);
ReaderInteractor <T> interactor = blockedReader as ReaderInteractor <T>;
if (interactor != null)
{
interactor.Fail(error);
}
else
{
((AutoResetAwaiter <T>)blockedReader).SetException(error);
}
}
// Complete a waiting reader if necessary. (We really shouldn't have both a blockedReader
// and a waitingReader, but it's more expensive to prevent it than to just tolerate it.)
if (waitingReader != null)
{
if (error != null)
{
waitingReader.Fail(error);
}
else
{
waitingReader.Success(false);
}
}
// Successfully completed the channel
return(true);
}
private Task WriteAsync(T item, CancellationToken cancellationToken = default(CancellationToken)) => cancellationToken.IsCancellationRequested ? Task.FromCanceled(cancellationToken) : TryWrite(item) ? Task.CompletedTask : Task.FromException(ChannelUtilities.CreateInvalidCompletionException(_doneWriting));